268 THE ARTICULATIONS OR JOINTS. 
neck of the scapula. By one end they are attached to the external border of the 
scapular spine, and by the other to the adjacent part of the posterior aspect of 
the head of the scapula. The suprascapular nerve and vessels pass subjacent to 
this ligament. 
THE SHOULDER-JOINT. 
The shoulder-joint (articulatio humeri) is one of the largest as well as the most 
important of the joints of the upper limb. It is an example of the enarthrodial, 
i.e. ball-and-socket variety of a diarthrosis, and, at the cost of a certain amount of 
security, it has obtained an extended range of movement. 
The bones which enter into its formation are the glenoid fossa of the scapula 
and the head of the humerus. 
The glenoid fossa is a shallow pyriform articular surface, having its narrow end 
directed upwards and slightly forwards. The upper half of the anterior margin of 
the fossa is characterised by a shallow notch which accommodates the narrow part 
of the subscapularis muscle as it runs outwards to its insertion. At the apex of the 
fossa there is a flat area for the attachment of the long tendon of the biceps flexor 
cubiti muscle. The head of the humerus is hemispherical and articular, while, 
external to its articular margin, there is a slight constriction (the anatomical or 
true neck of the humerus), which is most strongly marked in relation to the 
greater and lesser tuberosities of the humerus. 
Under ordinary conditions the two articular surfaces are maintained in 
apposition by muscular action, aided by atmospheric pressure, and thus, when the 
muscles are removed, the bones fall asunder to the full extent of the restraining 
ligaments. Only a small part of the humeral head is in contact with the glenoid 
fossa at any particular moment, because the former is much larger than the latter, 
but, by reason of the shallow character of this fossa, all parts of the two articular 
surfaces may successively be brought into contact with each other. 
In the position of rest, as the imb hangs parallel to the vertical axis of the 
trunk, the inferior aspect of the neck of the humerus is brought into close relation 
with the lower part of the glenoid fossa. 
The glenoid ligament (labrum glenoidale, Fig. 209) deepens the glenoid fossa, 
and thus extends the articular surface. It is situated within the joint capsule, and 
to some slight ex- 
tent increases the 
= a Coracohumeral  S@Curity of the arti- 
Ss <= P ligament culation. It con- 
| : 7 sists of a strong 
ring of dense fibrous 
tissue attached to 
the free margin of 
the glenoid fossa. 
3 Many of its fibres 
y Long are short, and pass 
of biceps obliquely from the 
inner to the outer 
aspect of the ridge, 
so that its attached 
base is broader than 
its free edge, and 
therefore in cross sec- 
\ tionitappears some- 
\ what triangular. 
Coraco-acromial ligament Acromion process 
Coracoid process 
Subscapularis 
- 
muscle 
Communication 
between subscapular 
bursa and joint cavity 
Capsule of joint ———- 
Fic, 208.—CaPsvLe OF THE SHOUEDER-soINT AND Coraco-acromran Licament, Lhe long tendon of 
the biceps, which 
arises from the apex of the glenoid fossa, becomes to a considerable extent in- 
corporated with this ligament. 
The capsular ligament (capsula articularis, Fig. 208) presents the general shape 
which is characteristic of the corresponding ligament in other ball-and-socket joints, 
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